1. Field of the Invention
The present invention relates to a motor driving technique, and particularly to a torque control technique thereof.
2. Description of the Related Art
In recent years, increase in the operation speed of personal computers and workstations has led to increase in the operation speeds of computation LSIs (large Scale Integrated Circuit) such as CPUs (Central Processing Unit), DSPs (Digital Signal Processor), etc.
Such LSIs have a problem in that an increase in the operation speed, i.e., an increase in clock frequency involves an increase in heat generation. The heat generation of the LSI leads to thermal runaway of the LSI itself, or affects its peripheral circuits, which becomes a problem. Accordingly, such a situation requires a suitable thermal cooling operation for the LSI, as a crucial technique.
Examples of techniques for cooling an LSI includes an air-cooling cooling method employing a cooling fan. In this method, for example, a cooling fan is arranged such that it faces the surface of the LSI, and cool air is blown onto the surface of the LSI using a cooling fan. When an LSI is cooled using a cooling fan, the temperature around the LSI is monitored, and the cooling operation is adjusted by changing the revolutions of the fan according to the temperature thus monitored (Patent documents 1 and 2).
Patent documents 3 through 5 disclose driving techniques for suitably setting the torque of a motor according to a target value of the revolution.
[Patent Document 1]
    Japanese Patent Application Laid Open No. H7-31190[Patent Document 2]    Japanese Patent Application Laid Open No. 2001-284868[Patent Document 3]    Japanese Patent Application Laid Open No. 2007-68344[Patent Document 4]    Japanese Patent Application Laid Open No. 2007-68347[Patent Document 5]    Japanese Patent Application Laid Open No. 2007-68348